UNDER FIRE: HHC chief Alan Aviles denies receiving complaints from women of harassment by a supervisor.

The municipal hospital system has hired an outside investigator to look into an allegation that its president, Alan Aviles, didn’t act on a complaint claiming a senior administrator was harassing and demeaning female employees.

The board of the Health and Hospitals Corp. made the decision to hire Guidepost Solutions, an international investigative agency, after the former supervisor of the HHC’s Inspector General’s Office sent a letter to several city officials requesting an independent audit of the office, where hundreds of cases are reportedly languishing.

The most explosive charge made in the letter was that two women working for the HHC notified Aviles that a senior administrator was continually battering them with filthy and derogatory language and Aviles did nothing to stop it.

“Instead of Aviles taking appropriate measures and alerting the IG, human resources or anyone in authority, he simply told his good friend [the senior administrator] about the complaint,” the letter asserted.

Aviles firmly denied anything of the sort happened.

“Not only did female employees never come to speak to me about something like this, but to this date I don’t know the identity of the complainant or complainants,” he told The Post on Friday.

According to Aviles, the first he heard of the matter was in June 2011, when the administrator told him some of his employees had been interviewed by Inspector General Norman Dion about the administrator’s allegedly “inappropriate remarks.”

“He [the administrator] denied that was the case,” Aviles recalled.

“It was several weeks later that I got a call from our IG informing me that there was an investigation . . . and that their initial impression was that the complainant was credible.”

The whistleblower told The Post that when Aviles did nothing, the frustrated women went to Dion, who got them to wear hidden microphones that caught the administrator in the act.

A couple of weeks before he was to be questioned by Dion, the administrator suddenly quit.

“He said he was resigning for personal reasons, that his father was frail and very ill and that he felt it was necessary for him to spend time with his father and his young son, his father’s grandson, because they might not have much time together,” said Aviles, who has served as HHC president since 2005.

“That’s all I know about it.”

Unlike every other investigative agency in the city subject to the Freedom of Information Law, the HHC inspector general until recently had refused to release information about closed investigations.

As a result, this highly unusual case was never made public.

After The Post exposed Dion’s secretive practice, the HHC revised its policy and ordered him to respond to all future Freedom of Information requests.

The HHC board also ordered Dion to provide an accounting of all open and closed cases by Nov. 5. Officials said the deadline wasn’t met because Dion’s office in lower Manhattan was among those evacuated by Superstorm Sandy.